It is known to scn a field of view with a detector which consists of a linear array of detector elements by deflecting the path of rays by means of an oscillating mirror, the image of the field of view being moved transversely to the longitudinal axis of the detector. With such a device one dimension of the scanned field of view is limited by the length of the detector. The other dimension is limited by the characteristics of the lens. Therefore only rather small fields of view can be scanned in this manner.
Furthermore it is known to scan a field of view along a rosette-shaped path by means of one single detector. The imaging and scanning optical system comprises first and second image deflecting means, which rotate at different rotary speeds. Usually the image deflecting means are mirrors which are inclined to the axis of rotation or optically refracting, rotating wedges (U.S. Pat. Nos. 4,039,246; 4,009,393; European patent application 79,684; U.S. Pat. Nos. 4,030,807 and 4,413,177) or systems of trihedral mirrors (U.S. Pat. No. 3,927,254). With such a rosette scan it takes a rather long time until all points of a rather large field of view have been traversed by a rosette loop at least once and the field of view has been scanned with the required resolution.
U.S. Pat. No. 4,393,408 shows a detector comprising a linear array of detector elements in combination with image rotating means. These image rotating means are formed by a rotating afocal system consisting of two cylindrical optical elements, which rotate about an axis perpendicular to the plane of their generatrices, and an optical element for focusing on the array of detector elements. The diameter of the field of view which can be scanned with such a rotary scanning device is determined by the length of the detector. Thus also with this prior art scanning device only rather small fields of view can be scanned.
European patent application 130,778 shows a rotary scanning device wherein an imaging optical system forms a stationary image of a field of view in the plane of a rotatable base element. The rotatable base element carries a linear array of detector elements. The image is scanned by rotating the base element.